To make the armature easier to handle, I mounted it in a block of wood left over from a flat pack DVD rack. The wire was then covered with a dilute solution of PVA and a few tweaks made to the position of some of the "branches".

For the bark I bought a small premixed bag of Artex from a well known DIY chain and mixed a small amount with the PVA and a drop of black poster paint borrowed from the kids arts and crafts box. The mixture was applied using a small paint brush and left to dry overnight before the process was repeated.

The bark was then painted with a mix of Tamiya acrylic Nos. XF-55 Dark Tan and XF-52 Flat Earth as a base. A dark wash of artist water colours (paynes grey and dark umber) was used to add depth and highlights picked out by dry brushing with Tamiya XF-53 Neutral Grey. The image below shows the over effect after painting.

A detail view of the tree trunk.

Detail of the branches.

After applying the bark and detailing, I feel the tree is looking better than my initial view of the armature and I think there are improvements I can make on future models. Next is to apply the foliage.